1. Field of the Invention
Exemplary aspects of the present invention relate to a guide device and an image forming apparatus, and more particularly, to a guide device for guiding a recording medium bearing a toner image and an image forming apparatus incorporating the guide device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
FIG. 1 illustrates a fixing device 20R installed in such image forming apparatuses, which includes a fixing roller 21R and an opposed pressing roller 22R that apply heat and pressure to a recording medium P bearing a toner image T. For example, the pressing roller 22R is pressed against the fixing roller 21R heated by a heater 32R disposed inside the fixing roller 21R to form a fixing nip NP therebetween through which the recording medium P bearing the toner image T is conveyed. As the fixing roller 21R and the pressing roller 22R rotate and convey the recording medium P through the fixing nip NP, the fixing roller 21R and the pressing roller 22R apply heat and pressure to the recording medium P, melting and fixing the toner image T on the recording medium P.
Thereafter, the recording medium P bearing the toner image T is discharged from the fixing device 20R while guided by a fixing exit guide 26R and a pressing exit guide 25R and conveyed through a guide device 40R incorporating a first conveyance path 1R created by a first conveyance wall plate 27R, a second conveyance wall plate 28R, and a third conveyance wall plate 29R in a recording medium conveyance direction D1 toward an output roller pair 17R. If a user selects single-sided printing, the recording medium P is discharged onto an output tray by the output roller pair 17R. Alternatively, if the user selects double-sided printing, immediately after the trailing edge of the recording medium P passes through a bifurcation 24, the trailing edge of the recording medium P springs toward a second conveyance path 2R by its rigidity. Before the tailing edge of the recording medium P reaches the output roller pair 17R, the output roller pair 17R reverses its direction of rotation, feeding the recording medium P toward the second conveyance path 2R. Thus, the recording medium P is conveyed through the second conveyance path 2R in a recording medium conveyance direction D2 while guided by duplex guide plates 30R and 34R constituting the second conveyance path 2R. Then, the recording medium P reenters the fixing device 20R where another toner image T is fixed on the back side of the recording medium P.
On the other hand, the image forming apparatus is requested to shorten a first print time from the time when the user enters a command to start a print job until the first recording medium P bearing the toner image T is discharged onto the output tray. To address such request, after the image forming apparatus is powered on or switched from a sleep mode to a print mode, the fixing roller 21R is configured to be heated to a predetermined fixing temperature in a shortened time. However, even when the fixing roller 21R is heated to the predetermined fixing temperature, the peripheral components of the fixing roller 21R, such as the first conveyance wall plate 27R and the duplex guide plates 30R and 34R, may be heated insufficiently. Accordingly, when an atmosphere heated by the fixing roller 21R moves to these cooler components, water droplets 31 may adhere thereto. If the water droplets 31 are transferred onto the recording medium P conveyed over the components adhered with the water droplets 31, they may damage the toner image T on the recording medium P.
To address this problem, several solutions are proposed to prevent transfer of the water droplets 31 to the recording medium P. For example, a guide plate mounting a plurality of convex ribs may be disposed downstream from the fixing roller 21R in the recording medium conveyance direction D1 so that the steps of each convex rib receive water droplets 31, thus minimizing an amount of water droplets 31 adhered to the top of the convex rib and therefore reducing the water droplets 31 that may be transferred onto the recording medium P. However, since it is difficult to suppress the height of the convex rib to ensure adequate strength, an insufficient interval may be provided between the water droplets 31 accumulated on the steps of the convex rib and the recording medium P passing over the convex rib, allowing the water droplets 31 to be transferred onto the recording medium P.
Alternatively, a guide plate mounting a plurality of wavy ribs may be disposed downstream from the fixing roller 21R in the recording medium conveyance direction D1 so that the wavy ribs minimize the contact area where they contact the recording medium P, thus reducing water droplets 31 adhering to the recording medium P. However, the recording medium P may get snagged on the wavy ribs and jammed.
Yet alternatively, the first conveyance wall plate 27R and the duplex guide plates 30R and 34R may be made of a thermal conductive material having a reduced heat capacity that facilitates heating of these plates and drying of water droplets 31 adhered thereto. However, such thermal conductive material may increase manufacturing costs.